The present invention relates to fabrication and rejuvenation of refractory metal parts, and more particularly to fabrication and rejuvenation of refractory metal parts at net shape or near shape with controlled microstructure.
Current processes for producing high purity refractory metal parts, such as sheets made from tantalum and tantalum alloys (for usage as sputtering targets, tube perform is, furnace part performs, etc.), include powder and ingot metallurgy. The ingot metallurgy process begins with selecting and blending suitable powders, pressing into bars and sintering. An electron beam or plasma or arc furnace is used to melt the bar and cool it into an ingot. The melting can be done in multiple steps. Electron beam melting and remelting removes impurities to produce an essentially pure tantalum ingot. Purities of 99.9% tantalum are routinely achieved. The ingot is thermomechanically processed and further cold or hot worked as needed (or cold worked with intermediate annealing) to produce a desired shape, such as plate, sheet, rod or fabricated part (hemisphere, semi-hemisphere, conical, dished sheet, cup, box, etc.). Components may also be machined directly from ingots 3.
This overall process is relatively slow and results in a final yield of approximately 40 to 60 percent. The sintering process consumes a significant amount of furnace time, but it is required to provide sufficient mechanical strength in the bars and is a preliminary deoxidation step for the refractory metal powder, such as tantalum. The bars are usually electron beam-melted under a hard vacuum to remove chemical impurities. The electron beam melting process can also consume a significant amount of furnace time and power, such as three electron beam guns at 105 kilowatts for 8 to 16 hours. Remelting is usually required which also consumes significant furnace time and power, such as four electron beam guns at 150 kilowatts for 8 to 16 hours.
Laser additive manufacturing (LAM) is a direct deposition process that uses a high power laser and powder feeding system to produce complex three-dimensional components from metal powders. The high power laser and multi-axis positioning system work directly from a CAD file to build up the component using a suitable metal powder. This process is similar to conventional rapid prototyping techniques, such as stereolithography and selective laser sintering (SLS), and laser welding. Laser welding was developed to join two components or to fabricate an article integral to a component. However, a fully dense metal component can only be made with such additional steps as casting or HIP'ing (hot isostatic pressing). Such a laser process has been developed to manufacture near-net shape titanium components for the aerospace industry. But a process does not exist for still higher melting refractory metals, such as tantalum.
Additionally, sputtering targets of high temperature materials, such as tantalum and other refractory metals (Ta, Nb, Ti, Mo, Zr, metals and alloys; hydrides, nitrides and other compounds thereof) used in integrated circuit manufacture and other electrical, magnetic and optical product manufacture usually are eroded in a non-uniform way during the process of sputtering which leads to a race track like trench on the operating side of the target. In order to prevent any contamination of substrates or catastrophic break-through of coolant fluids behind the target, the targets generally are withdrawn from service well before the refractory sputter metal is penetrated, accepting the need for a new target after only a minor portion of the sputter metal has been consumed. The major part of the sputter target can be resold only at scrap price or recycled with difficulty and apart from this, the backing plate of the target needs to be removed and may be re-bonded to a new sputter metal plate for recycling.
Consequently, there is a need to rejuvenate the refractory metal of the sputtering target to eliminate the need to recycle the whole target after only a minor share of the tantalum plate has been consumed.
It is an object of the present invention to provide a laser processing method for refractory metals and their alloys that produces a fully dense deposit that can be planar or curved with macro- and micro-mechanical properties at least equivalent to traditionally melted, consolidated, rolled and annealed parts.
It is a further object to increase yield recovery and otherwise decrease fabrication time and costs by net-shape or near-net shape fabrication.
It is a further object of the invention to decrease the recycling cost of refractory metal parts, such as tantalum plates for sputtering targets including their backing plate.
It is yet another object of the invention to reduce the cycle time between removing the refractory metal part, such as a sputtering target, from service and getting it back to service will be shortened.